Apparatus and method for performing handoff to reduce number of session transfers in a mobile communication system

ABSTRACT

A handoff apparatus and a method for reducing the number of session transfers in a mobile communication system are provided, in which an ANC determines whether a target ANT is included in an active set of the mobile communication system, establishes a connection session between the mobile communication system and an AT through a path connecting a target ANC of a different vendor and the target ANT if the target ANT is not included in the active set, and establishes the connection session between the mobile communication system and the AT through a path connecting the ANC and the target ANT if the target ANT is included in the active set.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit under 35 U.S.C. §119(a) of KoreanPatent Application No. 2006-0062646, filed on Jul. 4, 2006, in theKorean Intellectual Property Office, the entire disclosure of which ishereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and method for performinghandoff to reduce the number of session transfers in a mobilecommunication system. More particularly, the present invention relatesto an apparatus and method for reducing ping-pong-caused frequentsession transfers between Access Networks (ANs), when an Access Terminal(AT) moves to a Code Division Multiple Access (CDMA) 20001xEvolution-Data Only (EV-DO) network of a different vendor, with a CDMA2000 1xEV-DO packet session kept in a connected state.

2. Description of the Related Art

FIG. 1 illustrates a conventional session transfer method using two linklayer paths.

Referring to FIG. 1, when an AT 130 needs a handoff from a source cellto a target cell of a different vendor, another wired/wireless linklayer path is added for an activated RLP between a Packet Data ServingNode (PDSN) 110 and the AT 130 during a session transfer to the targetcell.

During transferring the RLP to the new wired/wireless link layer path, asession control and traffic process should be naturally handed over to aRadio Network Controller (RNC) 117 of the target cell and an existingconnection between an RNC 115 of the source cell and the PDSN 110 and anexisting connection between the RNC 115 and the AT 130 should bereleased.

Since separate RLPs are provided to the RNCs 115 and 117 during thesession transfer, the AT 130 can exchange user packets seamlessly onforward and reverse links.

Basically, the RNCs 115 and 117 of different vendors share a RadioNetwork Transceiver (RNT) 120 at a cell boundary and the two link layerpaths are maintained. That is, the single RNT 120 supportscommunications from the PDSN 110 to the AT 130 through the two linklayer paths for one RLP.

Due to the different link layer paths for the one RLP, headercompression such as Robust Header Compression (ROHC) is carried out inthe RNCs 115 and 117 to overcome the discrepancy between the link layerpaths.

In the illustrated case of FIG. 1, a wired/wireless link layer path isadded between the target RNC 117 and the RNT 120. The RNT 120 is sharedbetween the source RNC 115 and the target RNC 117.

This is done to maintain an existing radio traffic setting. When asession is transferred, a wired setting is mainly changed, while thechange of a wireless setting (i.e. the change of an active set) isminimal.

However, if handoff occurs frequently, that is ping-pong takes placebetween CDMA 2000 1xEV-DO networks of different vendors, the session isalso transferred frequently between the source RNC 115 and the targetRNC 117 at the boundary between the networks. As a result, callstability is impaired.

Also, when link layer paths are frequently set up for continual crossconnectivity between the target RNC 117 and all RNTs included in theactive set, load is added to the backhaul between the networks.

Although session information of the source RNC 115 and the old linklayer path between the source RNC 115 and RNTs included in the activeset can be maintained for some time during the session transfer forfrequent handoff, resource consumption may result.

Accordingly, there is a need for an improved apparatus and method forperforming handoff to reduce the number of session transfers in a mobilecommunication system.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention address at least theabove problems and/or disadvantages and provide at least the advantagesdescribed below. Accordingly, an aspect of exemplary embodiments of thepresent invention is to provide an apparatus and method for performing ahandoff with a reduced number of session transfers in a mobilecommunication system.

Another aspect of exemplary embodiments of the present invention is toprovide an apparatus and method for minimizing the number ofping-pong-caused session transfers when an AT moves to a mobilecommunication system of a different vendor, with a connection betweenthe AT and an AN maintained.

A further aspect of exemplary embodiments of the present invention is toprovide an apparatus and method for keeping Quality of Service (QoS) atthe same level, while keeping one RLP link during a handoff betweendifferent vendors in mobile communication systems of the differentvendors.

According to an aspect of exemplary embodiments of the presentinvention, there is provided a handoff method of an ANC for reducing thenumber of session transfers in a mobile communication system, in whichthe ANC determines whether a target ANT is included in an active set ofthe mobile communication system, establishes a connection sessionbetween the mobile communication system and an AT through a pathconnecting a target ANC of a different vendor and the target ANT, if thetarget ANT is not included in the active set, and establishes theconnection session between the mobile communication system and the ATthrough a path connecting the ANC and the target ANT, if the target ANTis included in the active set.

According to another aspect of exemplary embodiments of the presentinvention, there is provided a handoff method of an ANC for reducing thenumber of session transfers in a mobile communication system, in whichthe ANC bans an AT from changing session information, when a sessiontransfer to a target AN is determined, activates a session to the ATthrough the target AN by requesting a session allocation to a target ANCso that the target ANC performs a session setup procedure between a PDSNand a target ANT, and removes a session between the ANC and the PDSN.

According to a further aspect of exemplary embodiments of the presentinvention, there is provided a handoff apparatus of an ANC for reducingthe number of session transfers during a handoff in a mobilecommunication system, in which when an AT performs a handoff, a sessiontransfer processor establishes a connection session between the mobilecommunication system and the AT through a path connecting a target ANCof a different vendor and a target ANT if the target ANT is not includedin an active set, the session transfer processor establishes theconnection session between the mobile communication system and the ATthrough a path connecting the ANC and the target ANT if the target ANTis included in the active set, and a controller commands a sessiontransfer to the session transfer processor.

According to still another aspect of exemplary embodiments of thepresent invention, there is provided a handoff apparatus of an ANC forreducing the number of session transfers during a handoff in a mobilecommunication system, in which when an AT performs a handoff, a sessiontransfer processor bans the AT from changing session information,requests a session transfer to a target ANC of a different vendor sothat the target ANC performs a session setup procedure between a PDSNand a target ANT, and removes a session between the ANC and the PDSN,and a controller commands the session transfer to the session transferprocessor.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of certainembodiments of the present invention will become more apparent from thefollowing detailed description when taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates a conventional session transfer method using two linklayer paths;

FIG. 2 illustrates a session transfer that takes place after an ATcompletely moves to a target AN according to an exemplary embodiment ofthe present invention;

FIG. 3 is a diagram illustrating a signal flow for a session transferusing an existing RLP path according to an exemplary embodiment of thepresent invention; and

FIG. 4 is a block diagram of an AN apparatus for reducing the number ofsession transfers according to an exemplary embodiment of the presentinvention.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features, and structures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The matters defined in the description such as a detailed constructionand elements are provided to assist in a comprehensive understanding ofthe embodiments of the invention and are merely exemplary. Accordingly,those of ordinary skill in the art will recognize that various changesand modifications of the embodiments described herein can be madewithout departing from the scope and spirit of the invention. Also,descriptions of well-known functions and constructions are omitted forclarity and conciseness.

Exemplary embodiments of the present invention provide an apparatus andmethod for performing a handoff so as to reduce the number of sessiontransfers.

For this purpose, exemplary embodiments of the present invention supportsoft handoff between ANs of different vendors in CDMA 2000 1xEV-DOsystems of the different vendors based on cross connectivity and enablea source Access Network Controller (ANC) to control a target AT of adifferent vendor directly or indirectly.

Unlike a conventional session transfer based on Make Before Break (MBB)and cross connectivity between ANs of different vendors, a sessiontransfer takes place when sectors controlled by a target ANC disappearfrom an active set.

That is, exemplary embodiments of the present invention provide anapparatus and method for reducing ping-pong-caused frequent sessiontransfers, which is a problem encountered with the conventionaltechnology.

Also, exemplary embodiments of the present invention provide a methodfor providing a seamless handoff between different vendors using anexisting RLP path, compared to the conventional technology in which twolink layer paths are established for one RLP from a PDSN to an ATthrough source and target ANs.

In accordance with exemplary embodiments of the present invention, asession transfer occurs when an AT completely moves to a target AN. Thatis, a source ANC controls an on-going session until all the sectors ofthe source ANC are eliminated from the active set of the AT.

Herein, the term “AN” is used in the same sense as “Radio Network (RN)”and the term “ANC” is used in the same sense as “RNC”. The AN includesan ANC and an Access Network Transceiver (ANT) and the RN includes anRNC and an RNT.

FIG. 2 illustrates a session transfer that takes place after an ATcompletely moves to a target AN according to an embodiment of thepresent invention.

Referring to FIG. 2, even though an AT 230 moves to a service area of adifferent vendor, a source ANC 215 is kept connected to ANTs 220, 222,224 and 226 of service areas through which the AT 230 moves until asession transfer occurs.

When it is determined that the AT 230 is completely out of the servicearea of the source ANC 215, the session transfer takes place.

Since the session transfer is carried out after the AT 230 completelymoves into a target AN, without a connection setup based on crossconnectivity between the target AN and a source ANT that provides anexisting traffic channel, exemplary embodiments of the present inventioncan reduce frequent session transfers caused by ping-pong.

When the AT 230 moves to the service area of a system of a differentvendor in a connected state, service continuity can be ensured by crossconnectivity-based soft handoff.

However, an increase in the load of a backhaul network due to relayingof user packets between different vendors and a transmission delaydecrease QoS, which can be a problem to users and operators.

Therefore, it is necessary to transfer a session when the AT 230 hasmoved to the target AN. That is, the AT 230 performs soft handoff andthen moves to the target AN in steps b) and d). Then, in steps c) andd), the AT 230 updates a link layer path. In this case, PDSNs 210 and212 can be shared by different vendors.

The session transfer is carried out only when the AT 230 moves to asector which is not included in an active set.

Now a description will be made of a technique for supporting a seamlesshandoff through a single wired/wireless link layer path according to anexemplary embodiment of the present invention.

In the conventional two routes per RLP technology, an additionalwired/wireless link layer path is established from a PDSN to an AT.Therefore, only Signaling Layer Protocol (SLP) information processed ina source AN has to be transmitted to a target AN during a sessiontransfer.

In contrast, exemplary embodiments of the present invention still use anexisting RLP path.

FIG. 3 is a diagram illustrating a signal flow for a session transferusing an existing RLP path according to an exemplary embodiment of thepresent invention.

Referring to FIG. 3, an AT 330 is receiving a service through a sourceAN 315 in step 300. When the AT 330 moves to a target AN 317, itperforms a soft handoff from a source ANT to a target ANT by crossconnectivity.

If the AT 330 determines that a session transfer is required due to themovement to the target AN 317 in step 301, a session allocationprocedure is performed in step 302.

If the session transfer to the target AN 317 is possible, the source AN315 locks a session so as to prevent the AT 330 from changing sessioninformation in step 303 and requests the session transfer to the targetAN 317 by an A13 Session Transfer Request message in step 304.

In this case, information about ANTs connected by cross connectivity isalso transmitted. Then, the target AN 317 requests an A10 connection toa PDSN 310 in step 305 and establishes a wired/wireless link layer pathto ANTs in step 306.

When the establishment is successful, the target AN 317 transmits an A13Session Transfer Response message to the source AN 315, notifying thesession transfer success in step 307.

In step 308, the source AN 315 transmits XOFF to the PDSN 310. The PDSN310 changes a current A10 connection to the target AN 317 in step 309.Then traffic transmission/reception starts between the PDSN 310 and thetarget AN 317.

In step 310, the source AN 315 provides SLP information and finalprocessed RLP information (e.g. sequence information) to the target AN317 by an A13 Session Transfer Complete message, thus completing thesession transfer.

The target AN 317 activates the link layer path of an ANT, thusconnecting a wireless path between the AT 330 and the ANT to a wiredpath between the target AN 317 to the PDSN 310 in step 311.

In step 312, the target AN 317 replies to the source AN 315 with an A13Session Transfer Complete Ack message. The source AN 315 forwards userpackets received from the PDSN 310 temporarily after step 308 to thetarget AN 317.

The target AN 317 starts a signaling control and traffic processingoperation based on the SLP and RLP information received from the sourceAN 315.

The target AN 317 allocates a new Unicast Access Terminal Identifier(UATI) to the AT 330 in step 313. Almost at the same time, the PDSN 310transmits an A11 Registration Update message to the source AN 315,releasing the A10 connection, when the A10 connection is not required instep 314. Then the session transfer is completed and the session ismanaged by the target AN 317 in step 315.

The source AN 315 transmits to the target AN 117 additional processinginformation about traffic to which header compression like ROHC isapplied to in step 304.

During the session transfer, the source AN 315 forwards user packetsreceived from the PDSN 310 to the target AN 317 for a predetermined timeperiod. Therefore, packet loss that may occur during the sessiontransfer from the source AN 315 to the target AN 317 is minimized.

The above-described session transfer mechanism in FIG. 2 of an exemplaryembodiment of the present invention is suitable for an applicationservice to which transmission itself is important, such as File TransferProtocol (FTP), in that a session transfer takes place only after an ATcompletely moves to a target AN, that is, a source ANC keeps its controlas long as possible.

The session transfer mechanism in FIG. 3 of an exemplary embodiment ofthe present invention also ensures sufficient QoS for an applicationservice that tolerates partial packet loss and out-of-order delivery,such as Voice over Internet Protocol (VoIP), in that a single link layerpath is used.

FIG. 4 is a block diagram of an AN apparatus for reducing the number ofsession transfers according to an embodiment of the present invention.

Referring to FIG. 4, a controller 440 provides overall control to the ANapparatus. For example, the controller 440 processes and controls voicecommunication and data communication. In addition to its typicalfunctionalities, the controller 440 performs a handoff between differentvendors. If a session transfer is required during the handoff, thecontroller 440 controls a session transfer processor 420 to decide on asession transfer scheme and performs the session transfer in the sessiontransfer scheme according to an exemplary embodiment of the presentinvention.

Depending on whether the decided session transfer scheme is to performthe session transfer by changing a session transfer time or to support aseamless handoff via a single link layer path and perform the sessiontransfer correspondingly, the controller 440 performs the sessiontransfer accordingly.

The session transfer processor 420 decides on the session transferscheme under the control of the controller 440 and notifies thecontroller 440 of the decided session transfer scheme.

For example, for an application service whose transmission itself issignificant, such as FTP, the session transfer processor 420 decides ona session transfer scheme that changes a session transfer time to afteran AT completely moves to a new AN. For an application service thattolerates partial packet loss and out-of-order delivery, such as VoIP,the session transfer processor 420 can decide on a session transferscheme that uses a single link layer path. This decision method is notfixed and thus other methods are also available. Also, only one of thetwo session transfer schemes can be used.

A storage 430 stores programs for controlling the AN apparatus andtemporarily stores data generated during program execution.

An interface module 410 is used to communicate with a higher-layernetwork or an AT. For communicating with the AT, the interface module410 includes a Radio Frequency (RF) processor and a baseband processor.

The RF processor downconverts an RF signal received through an antennato a baseband signal and provides the baseband signal to the basebandprocessor. It also upconverts a baseband signal received from thebaseband processor to an RF signal transmittable in the air andtransmits the RF signal through the antenna.

In CDMA, for example, the baseband processor channel-encodes and spreadstransmission data during transmission. It despreads and channel-decodesa received signal during reception.

For communicating with the higher-layer network, the interface module410 includes a baseband processor and a wired processor. Manytechnologies including optical communications can be applied to aphysical transmission interface used by the wired processor.

The controller 440 controls the session transfer processor 420. That is,the controller 440 can perform the functions of the session transferprocessor 420. While the controller 440 and the session transferprocessor 420 are shown separately for illustrative purposes, thesession transfer processor 420 can be wholly or partially incorporatedinto the controller 440 in real implementation. Also, separate means canbe configured for performing individual operation steps or these meanscan be incorporated into the controller 440.

As described above, exemplary embodiments of the present inventionadvantageously minimize the number of ping-pong-caused frequent sessiontransfers by changing a session transfer time to after an AT moves to atarget AN.

Without a connection setup between the target AN and a source AN in theconventional cross connectivity structure, exemplary embodiments of thepresent invention reduce unnecessary traffic transmission/reception onthe backhaul between different vendors.

Further, exemplary embodiments of the present invention provide aseamless handoff between different vendors, while keeping a singlewired/wireless link layer path in a connected state. Therefore,exemplary embodiments of the present invention can be easilyimplemented.

The present invention can also be embodied as computer-readable codes ona computer-readable recording medium. The computer-readable recordingmedium is any data storage device that can store data which canthereafter be read by a computer system. Examples of thecomputer-readable recording medium include, but are not limited to,read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetictapes, floppy disks, optical data storage devices, and carrier waves(such as data transmission through the Internet via wired or wirelesstransmission paths). The computer-readable recording medium can also bedistributed over network-coupled computer systems so that thecomputer-readable code is stored and executed in a distributed fashion.Also, functional programs, codes, and code segments for accomplishingthe present invention can be easily construed as within the scope of theinvention by programmers skilled in the art to which the presentinvention pertains.

While certain exemplary embodiments of the invention have been shown anddescribed with reference to certain preferred embodiments thereof, itwill be understood by those skilled in the art that various changes inform and details may be made therein without departing from the spiritand scope of the invention as defined by the appended claims and theirequivalents.

1. A handoff method for reducing the number of session transfers in a mobile communication system, comprising the steps of: determining whether a target Access Network Transceiver (ANT) of a different vendor is included in an active set of the mobile communication system; if the target ANT of the different vendor is not included in the active set, establishing a connection session between a Packet Data Serving Node (PDSN) and an Access Terminal (AT) through a path connecting a source Access Network Controller (ANC) and a target ANC of the different vendor and a path connecting the target ANC of the different vendor and the target ANT of the different vendor; and if the target ANT is included in the active set, establishing the connection session between the PDSN and the AT through a path connecting the source ANC and the target ANT of the different vendor.
 2. The handoff method of claim 1, wherein the source ANC and the target ANC of the different vendor share the PDSN.
 3. A handoff apparatus of a source Access Network Controller (ANC) for reducing the number of session transfers during a handoff in a mobile communication system, comprising: a session transfer processor for determining whether a target Access Network Transceiver (ANT) of a different vendor is included in an active set of the mobile communication system, if the target ANT of the different vendor is not included in the active set, sending a request to establish a connection session between a Packet Data Serving Node (PDSN) and an Access Terminal (AT) through a path connecting the source ANC and a target ANC of the different vendor and a path connecting the target ANC of the different vendor and the target ANT of the different vendor and establishing a path connecting the source ANC and the target ANC, if the target ANT is included in the active set, establishing the connection session between the PDSN and the AT through a path connecting the source ANC and the target ANT of the different vendor; a controller for commanding a session transfer to the session transfer processor.
 4. The handoff apparatus of claim 3, wherein the source ANC and the target ANC of the different vendor share the PDSN.
 5. The handoff apparatus of claim 3, wherein the session transfer processor supports the handoff seamlessly by maintaining an old path during the handoff.
 6. A handoff method of a source Access Network Controller (ANC) for reducing the number of session transfers during a handoff in a mobile communication system, comprising: determining whether a target Access Network Transceiver (ANT) of a different vendor is included in an active set of the mobile communication system; if the target ANT is not included in the active set, sending a request to a target ANC of the different vendor for establishing a connection session between a Packet Data Serving Node (PDSN) and an Access Terminal (AT) through a path connecting the source ANC and the target ANC of the different vendor and a path connecting the target ANC of the different vendor and the target ANT of the different vendor; establishing a path connecting the source ANC and the target ANC; and if the target ANT is included in the active set, establishing the connection session between the PDSN and the AT through a path connecting a source ANC and the target ANT of the different vendor.
 7. The handoff method of claim 6, wherein the source ANC and the target ANC of the different vendor share the PDSN.
 8. A handoff system for reducing the number of session transfers in a mobile communication system, comprising: a source Access Network Controller (ANC) for determining whether a target Access Network Transceiver (ANT) of a different vendor is included in an active set of the mobile communication system, if the target ANT of the different vendor is not included in the active set, sending a request to a target ANC of the different vendor for establishing a connection session between a Packet Data Serving Node (PDSN) and an Access Terminal (AT) through a path connecting the source ANC and the target ANC of the different vendor and a path connecting the target ANC of the different vendor and the target ANT of the different vendor and establishing a path connecting the source ANC and the target ANC, if the target ANT is included in the active set, establishing the connection session between the PDSN and the AT through a path connecting the source ANC and the target ANT of the different vendor; and the target ANC for determining whether to receive the request from the source ANC, if the target ANC receive the request, establishing a connection session between the PDSN and the AT through a path connecting the target ANC of the different vendor and the target Access Network Transceiver (ANT) of the different vendor.
 9. The handoff system of claim 8, wherein the source ANC and the target ANC of the different vendor share the PDSN.
 10. A handoff apparatus of a source Access Network Controller (ANC) for reducing the number of session transfers during a handoff in a mobile communication system, comprising: means for determining whether a target Access Network Transceiver (ANT) of a different vendor is included in an active set of the mobile communication system; means for sending a request to a target ANC of the different vendor for establishing a connection session between a Packet Data Serving Node (PDSN) and an Access Terminal (AT) through a path connecting the source ANC and a target ANC of the different vendor and a path connecting the target ANC of the different vendor and the target ANT of the different vendor if the target ANT is not included in the active set; means for establishing a path connecting the source ANC and the target ANC if the target ANT is not included in the active set; and means for establishing the connection session between the PDSN and the AT through a path connecting the source ANC and the target ANT of the different vendor, if the target ANT is included in the active set.
 11. The handoff apparatus of claim 10, wherein the source ANC and the target ANC of the different vendor share the PDSN. 